Lab 4 Outline

• This lab we’ll talk about the energy budget on the earth’s surface.

• 1. Some radiation laws: Stephan-Boltzmann law (amount) and Wien’s law-(character, i.e., wavelength).

• 2. Some factors of radiation fluxes, i.e., solar and terrestrial in-coming and outgoing radiation (e.g. albedo).

• 3. Some basic surface energy budget calculations using net surface radiation formula.

• 4. Radiation and season, time of day, cloudiness, etc.

The Surface Energy Budget• Surface energy budget: how much energy is

coming to the earth versus going out. • Radiation: mechanism of heat transfer w/out a

medium (unlike conduction and convection).• Recall some solar radiation receipt factors:

1. Seasonal2. Diurnal (daily)3. Meteorological influences

Three types of heat transfer:

1.Conduction – requires a medium in which to travel

2.Convection – requires a medium in which to travel

3.Radiation – the only mechanism of heat transfer that travels through space.

The sun is the ultimate source of energy that drives all our weather.

Radiation Laws - Amount

1. Stefan-Boltzmann law:– Total energy EMITTED by a body is

proportional to temperature

300 K

6000 K

The WARMER the surface, the more radiation is emitted.

The WARMER the surface, the more radiation is emitted.

The Surface Energy Budget

• The Earth:– Surface temperature = 288K (15°C)

2554 = 4,228,000,000

E = 5.67 Wm-2 x 42.28

5.67 x 10-8 = 0.0000000567

Radiation Laws: Character2. Wien’s law:

– Radiation wavelength is inversely proportional to T°

C = 2898ϻmKT K

Wien’s constant

TYPE OF ENERGY WAVELENGTH (ϻm)

Gamma <0.0001

X-ray 0.0001 to 0.01

Ultraviolet (UV) 0.01 to 0.4

Visible 0.4 to 0.7

Near infrared (NIR) 0.7 to 4.0

Thermal infrared 4 to 100

Microwave 100 to 1,000,000

Warmer temps = SHORTER wavelengthsWarmer temps = SHORTER wavelengths

• Sun’s wavelength falls under the visible spectrum….which explains the glow we always see around it.

• Earth’s wavelength falls under the thermal infared spectrum.

Radiation Fluxes• Radiation budget is made up of the four fluxes

• Net surface radiation = SW↓ - SW↑ + LW↓ - LW↑• Note: SW only a factor while the sun in out

SWSW LW LWDepends on location,

time of year, time of day, cloudiness, etc. Depends on surface

temperature.

Depends on the state of the atmosphere.Depends on surface albedo.

• SW radiation fluxes only relevant between sunrise and sunset

• LW radiation fluxes occur throughout the entire day

• LW↑ will always be greater/higher than LW↓;

• SW↓ will always be greater/higher than SW↑; some of the incoming radiation will always be absorbed by the earth, reducing the amount that is re-emitted.

Albedo – outgoing sw factor

Light colors reflect more than dark colors.• dark colors have a LOW albedo…they only reflect 10-15% of the radiation (they absorb 20-85%)• light colors have a HIGH albedo…they reflect 50-90% of the radiation (they absorb 10-50%)

The Surface Energy Budget

BEFORE

**Diagram is of an equinox

SW solar radiationLW terrestrial radiation

Cloudy skies = LOWER SWClear skies = HIGHER SW

Cloudy skies = LOWER SWClear skies = HIGHER SW